Something not composite cannot be a composite of actual and possible, and so must be either just actual or just possible. But something cannot be just possible with no actual existence, because it would simultaneously not exist (because it has no actual existence) and exist (because it is an existing thing that is only possible).
So a non-composite thing must be purely actual. That is, no capability for change even in principle. It has no parts whatsoever. What would it be like?
Non-Physical: It could not be composed of matter or energy, because matter and energy are both changeable and are hence composed of the actual and the possible.
Spaceless: It could not be located in any particular location in space, because then it would be changeable in principle, and hence a mixture of actual and possible.
Timeless: It could not be located within time, because then it would be possibly older than it is now. But it has no possibilities. So it is timeless.
One: Because it is timeless and spaceless, all beings of pure actuality are the same being. Also, if there were more than one such being, there would be some way of telling them apart and so one would have a feature that the other lacked (such as location, size, etc). But something of pure actuality has no unrealized possibilities, and so it lacks nothing. So all beings of pure actuality are one.
Omnipotent: As the causal source of anything that ever occurs or could occur, it can do anything. In addition, if there were things it could not do, then this would be an unrealized possibility, which it does not have.
Omniscient: As the thing that makes all facts true and keeps everything in existence, it does not have knowledge but rather is knowledge itself. In addition, if it possessed less than absolute knowledge, it could possibly learn more. But something that is purely actual has no unrealized possibilities. This topic will also be revisited in future posts.
Perfect: As we saw in part 1 and part 3, there must be not just individuals, but structure or types as well. So each individual (such as Mt St Helens) belongs to a category or type (volcanoes). But each individual has flaws that make it an imperfect version of its archetype. An individual dog, for example, will have injuries, or a gimpy leg, or perhaps just flaws on the cellular level that make it an imperfect version of a dog. So when we speak of "perfection", we mean "getting as close as possible to its archetype". A thing of pure actuality, then, is perfect in the sense that it doesn't lack anything, or have any flaws. If it did. these would be unrealized possibilities, which it doesn't have by definition.
Simple: "Complex" means "consisting of many different and connected parts." And "simple" means "having or composed of only one thing, element, or part." But the non-composite thing is not composed of parts, so it is simple.
As you can see, from the mere fact that things change, come into and go out of existence, and are composites of the actual and the possible, there is a sustaining force that is spaceless, timeless, immaterial, One, simple, omnipotent, omniscient, and perfect. This everyone calls "God."